OBJECTIVES: To investigate the feasibility, validity and reliability of the Welsh language version of the EQ-5D in a random adult population sample in Welsh-speaking areas of Wales. METHODS: 1000 names were selected at random from electoral registries, and questionnaires that included the Welsh version of the EQ-5D together with questions on socio-economic, demographic and health status, were mailed. Subjects were asked to rate their health on the day of completion. Respondents to the first questionnaire were sent a second EQ-5D within a fortnight to assess test-retest reliability. A reminder was sent if the second questionnaire was not returned within a fortnight. A pre-paid envelope was provided in each case. The acceptability and feasibility was assessed by examining the number of missing responses on returned forms. A reliability analysis was conducted, following the test-retest procedure, and construct validity was assessed in terms of convergent validity. RESULTS: 126 subjects returned the first questionnaire, of which 113 completed the second. Women represented 59.9% of the sample, and respondents' mean age was 56.8 +/-18 years. 38.7% of subjects reported having chronic illness. The number of missing items from the descriptive EQ-5D (aggregated for both administrations) was 4, representing 0.33% of all responses. Five EQ-VAS responses were returned incomplete. 97 (85.8%) respondents reported no change in health in the fortnight between the first and second administration. The Spearman rank coefficients for these respondents were 0.828 for EQ-5D scores, and 0.815 for EQ-VAS, respectively (both p<0.000). The results of the regression analysis for convergent validity suggested that, together, EQ-VAS score, self-reported health (5-point Likert scale; poor to excellent), presence of chronic illness, and receipt of treatment, explained 66.0% of the variation in EQ-5D scores. CONCLUSION: It is concluded that the Welsh version of the EQ-5D has good acceptability, validity and reliability in measuring health status in subjects across Wales.